A method of plasma-arc welding of metals using the so-called constricted arc (cf. a textbook "Microplasma-arc welding" ed. by B. Ye. Patton, Ukraine, Kiev, "Naukova dumka" publishers, 1979, pp.19-21 (in Russian). The essence of the method resides in that the arc discharge occurs in a stream of inert gas between the cathode of the plasma-arc welding torch of a plasmatron and the workpiece--anode, while the diameter of the arc discharge is restricted to the torch nozzle passage. Insofar as direct arc striking between the electrode and the workpiece across a narrow nozzle passage is difficult, first a pilot arc is initiated between the electrode and the torch nozzle--anode, whereupon an inert gas is fed thereto.
While being under pressure said gas emerges from the outlet of the nozzle--anode to establish a plasma jet due to constriction of the pilot arc. As soon as the plasma jet contacts the workpiece the main arc is started. In this case the pilot arc may persist, thus stabilizing the main arc under low-amperage conditions. While controlling the consumption rate of the plasma-producer gas, one can vary the pressure exerted on the molten weld pool and hence the depth of penetration of the workpiece--anode.
The afore-discussed known method is instrumental in obtaining quality weld joints; however, provision of an external inert-gas source involves some operational inconveniences in carrying said method into effect, while high production cost of the inert gas and considerable expenses for charging gas bottles and their delivery impose substantial limitation on practical applicability of the aforementioned method of plasma-arc welding.